1. Field of the Invention
The present invention relates to a soldering apparatus and a soldering method, e.g., a soldering apparatus and a soldering method with which flow soldering on an electronic circuit board on which a flux having water as a solvent is applied is performed while removing water from the electronic circuit board.
2. Related art of the Invention
A conventional apparatus for soldering on an electronic circuit board is constituted by a fluxer which applies a flux, a heating device for causing the applied flux to exert activating action, a flow solder bath for attaching molten solder to a surface to be soldered, and a cooler for cooling the soldered circuit board. Flow soldering has been performed by using this apparatus.
The flux used in this soldering is obtained by dissolving solid components such as rosin and an activator in a solvent and is applied to a surface of an electronic circuit board to be soldered by a foaming fluxer or a spray fluxer. The applied flux is heated so as to be maintained at a state of a temperature of 100 to 150° C. to evaporate the solvent. By exerting the action of the activator in this state, the surface of the electronic circuit board to be soldered can be cleaned. Unless this heating is performed, the surface to be soldered is not cleaned and a good soldered surface cannot be obtained by bringing the surface to be soldered into contact with the molten solder in the flow solder bath.
In the solvent of the above-described flux, alcohol such as isopropyl alcohol is used. Solvents such as alcohol (volatile organic compounds: VOC), however, are decomposed by ultraviolet rays or the like when released into the atmosphere. Radicals are thereby formed to act as a cause of photochemical smog. Therefore, the development of fluxes having reduced amounts of VOCs or using no VOCs is being pursued.
FIG. 12 is a diagram showing an arrangement for a soldering apparatus described in Japanese Patent Laid-Open No. 2005-203582. As shown in FIG. 12, a soldering apparatus 200 has an arrangement in which a fluxer 1, a first heating device 2, a second heating device 3, a flow solder bath 4 and a cooler 5 are successively disposed along a direction A of movement of a conveyor 8 which conveys electronic circuit boards (not shown). The second heating device 3, the flow solder bath 4 and the cooler 5 are integrally housed in one unit.
In Japanese Patent Laid-Open No. 2005-203582, a flow soldering method using the soldering apparatus 200 shown in FIG. 12 and applicable with a flux having water as a solvent is described. The soldering apparatus 200 uses, as a method of removing the water content of a flux having water as a solvent and applied to an electronic circuit board by the fluxer 1, the first heating device 2 using far infrared rays and hot air in combination. That is, the first heating device 2 has the function of efficiently removing water applied to an electronic circuit board by the fluxer 1.
On the electronic circuit board passed through the first heating device 2, the activating action of the flux is exerted by the second heating device 3. In the flow solder bath 4, soldering is performed on the electronic circuit board passed through the second heating device 3 by bringing molten solder into contact with a surface of the electronic circuit board to be soldered. After soldering, the electronic circuit board is cooled by the cooler 5. By these steps, soldering is completed.
FIG. 13 is a diagram showing another arrangement for a soldering apparatus described in Japanese Patent Laid-Open No. 2005-203582. As shown in FIG. 13, a soldering apparatus 300 has an arrangement in which a vacuum drying device 6 is provided between a fluxer 1 and a second heating device 3.
A flow soldering method using the soldering apparatus 300 and applicable with a flux having water as a solvent is described. The soldering apparatus 300 uses the vacuum drying device 6 as a method of removing the water content of a flux having water as a solvent and applied to an electronic circuit board by the fluxer 1. The vacuum drying device 6 uses the effect of removing water as described below. The vacuum drying device 6 puts in a chamber 6a an electronic circuit board (not shown) to which a flux having water as a solvent has been applied, and subjects the electronic circuit board to a reduced pressure to reduce the boiling point of water, thereby removing the water content. On the electronic circuit board after processing with the vacuum drying device 6, the activating action of the applied flux is exerted by the second heating device 3. In the flow solder bath 4, soldering is performed on the electronic circuit board passed through the second heating device 3 by bringing molten solder into contact with a surface of the electronic circuit board to be soldered. After soldering, the electronic circuit board is cooled by the cooler 5. By these steps, soldering is completed.
The above-described conventional soldering apparatuses and methods, however, have problems described below.
In the above-described arrangement shown in FIG. 12, a heating device using far infrared rays and hot air in combination is used as the first heating device 2. It is necessary to heat in the first heating device 2 an electronic circuit board to which a flux having water as a solvent has been applied by the fluxer 1 until the water content in the flux is completely removed by drying with hot air effective in drying up water.
In this case, however, a time of about 120 seconds is required to increase the temperature of the electronic circuit board to the desired temperature in order to completely evaporate water attached to the electronic circuit board.
On the other hand, if the electronic circuit board is left in the first heating device 2 for an excessively long time in an attempt to completely evaporate attached water, there is a risk of the temperatures of low-heat-resistant components on the electronic circuit board being increased above the heat resistance temperatures to damage the components.
In actuality, therefore, it is difficult to continue putting an electronic circuit board in the first heating device 2 until the water content of a flux having water as a solvent is completely removed from the electronic circuit board. After all, actual use of the conventional soldering apparatus 200 and soldering method shown in FIG. 12 entails a problem that part of the water content of a flux remains on an electronic circuit board before soldering.
If water on the electronic circuit board cannot be completely removed by the first heating device 2, a good soldered surface cannot be obtained by performing heating with the second heating device 3 and bringing the electronic circuit board into contact with molten solder in the high-temperature flow solder bath 4. If water cannot be sufficiently removed, the activation by the flux component cannot be sufficiently exerted in the second heating device 3 and oxides on the substrate surface cannot be removed. That is, failure to sufficiently wet the electronic circuit board with solder occurs.
Further, if the water content of the flux having water as a solvent cannot be completely removed in the second heating device 3, water not removed is evaporated by an abrupt increase in temperature in the flow solder bath 4 to scatter solder, thereby causing a solder ball defect.
The above-described problem that part of the water content of a flux remains on an electronic circuit board has been observed, for example, particularly as a phenomenon in which film of water is formed so as to cover vent holes in an electronic circuit board and gaps between leads of electronic component parts and peripheral portions of holes in which the electronic component parts are inserted.
In the arrangement for the soldering apparatus 300 shown in FIG. 13, the vacuum drying device 6 is used for drying. The vacuum drying device 6 utilizes the phenomenon in which the boiling point of water is reduced under a reduced pressure. With this arrangement, each of electronic circuit boards is subjected to a reduced pressure in the chamber of the vacuum drying device 6 after a flux having water as a solvent has been applied by the fluxer 1.
In this case, however, it is difficult to perform the preceding step using the fluxer 1 and the subsequent step using the second heating device 3 in an in-line manner, i.e., as operations on the conveyor 8.
This is because there is a need for operations including an operation to remove the electronic circuit board once from the line after the completion of the step using the fluxer 1, an operation to reduce the pressure, an operation to maintain the reduced pressure, and an operation to return the pressure to ordinary pressure after putting an electronic circuit board in the vacuum drying device 6, and because a time of at least about 600 seconds is taken before the completion of removal of water from the electronic circuit board. In actuality, therefore, it is difficult to continue putting an electronic circuit board in the vacuum drying device 6 until the water content of a flux having water as a solvent is completely removed from the electronic circuit board, as in the case of the arrangement shown in FIG. 12. Therefore, actual use of the conventional soldering apparatus and soldering method shown in FIG. 13 entails a problem that part of the water content of a flux remains on an electronic circuit board before soldering, as in the case of the arrangement shown in FIG. 12.
In view of the above-described problem of the conventional art, an object of the present invention is to provide a soldering apparatus and method which can be used so that no part of the water content of a flux remains on an electronic circuit board before soldering.